The present invention relates to an improved metal-to-metal stem seal for sealing between the exterior of a movable valve stem and the interior of the bore through which the stem extends.
Prior to the present invention there have been many stem seals which have been tried but they have suffered from some disadvantage. For example, some of the prior seals have caused galling of the stem. Others have not provided a continuous seal either due to losing their preferred configuration when exposed to excess pressure either in testing or in service or have worn prematurely so that the metal surfaces no longer were in sealing contact.
An example of a metal-to-metal seal which has been used both in stem sealing applications and in the sealing of the annulus between a casing hanger and the surrounding housing is disclosed in Paper No. OTC 4371 presented at the 14th Annual Offshore Technology Conference in Houston, Tex., May 3-6, 1982 and entitled "Fire Resistant Wellhead Equipment for Statfjord `B` Platform". The specific metal seal ring which is referred to above is that seal labelled "Primary Seal" in FIG. 7 of such paper. The seal has inner and outer legs extending from a midpoint in the seal ring base portion and diverging from each other. The seal legs end in a reverse curve so that their outer end are convergent with respect to each other. The seal ring labelled "Secondary Seal" us a U shaped seal ring having an energizing ring which urges the outer ends of the seal legs into sealing engagement with the walls of the annulus against which they are to seal.
Another similar shaft seal is disclosed in U.S. Pat. No. 4,471,965 in which the seal ring is U-shaped in section and the two legs each have an outer rounded projection which is intended to make the sealing contact with the surface against which it is to seal.